Fuel compositions for vehicles are continually being improved to enhance various properties of the fuels in order to accommodate their use in newer, more advanced engines. Often, improvements in fuel compositions center around improved fuel additives and other components used in the fuel. For example, friction modifiers may be added to fuel to reduce friction and wear in the fuel delivery systems of an engine. Other additives may be included to reduce the corrosion potential of the fuel or to improve the conductivity properties. Still other additives may be blended with the fuel to improve fuel economy. Engine and fuel delivery system deposits represent another concern with modern combustion engines, and therefore other fuel additives often include various deposit control additives to control and/or mitigate engine deposit problems. Thus, fuel compositions typically include a complex mixture of additives.
However, there remain challenges when attempting to balance such a complex assortment of additives. For example, some of the conventional fuel additives may be beneficial for one characteristic, but at the same time be detrimental to another characteristic of the fuel. Other fuel additives often require an unreasonably high treat rate to achieve their desired effect, which tends to place undesirable limits on the available amounts of other additives in the fuel composition.
Quaternary ammonium compounds, such as alkoxylated salts, have recently been developed as detergents for fuels. The quaternary ammonium compounds, in some instances, are obtained from an acylating agent reacted with a polyamine, which is then alkylated or quaternized by a quaternizing agent. While providing improved detergency compared to prior detergents, these quaternary ammonium compounds and their methods of alkylation, however, still have several shortcomings. For example, in some instances, ethylene oxides and propylene oxides are used to make such detergents. Such oxides, however, are often undesired due to their handling difficulties. Quaternary ammonium compounds may also be formed through alkylation using dialkyl carbonates. However, the carbonate anion may be susceptible to precipitation and drop out of certain types of fuels or fuel additive packages. Other quaternary ammonium salts require halogenated carboxylic acids as quaternary agents. These salts may include residual halogens that may be less preferred in some applications. In yet other instances, removing undesirable ash generating components from the quaternizing manufacturing process is complicated.
While offering an improvement in detergency, prior quaternary ammonium compounds still have limitations in that relatively higher treat rates may be required to achieve adequate detergency effect in some applications. Often the pendant quaternary nitrogen in the quaternary ammonium salt is a derived from a diamine, such as dimethylamino propylamine, a common tertiary diamine obtained from the Michael reaction between dimethylamine and acrylonitrile through a subsequent hydrogenation. This diamine is a commonly available and convenient amine to form a quaternary ammonium salt. However, when using such tertiary amine source in a quaternizing reaction, it is often hindered in its availability for alkylation and/or activity as a detergent. As a result, quaternary ammonium salts obtained from such tertiary amines may not be sufficiently effective for improving injector performance at relatively low treat rates.